CHARACTERIZATION OF CAMEL MILK WHEY PROTEINS

Abstract

The present study was undertaken to characterize camel milk whey proteins. The main objective has been the isolation, purification and structure elucidation of protein components in whey, which comprise known classes of milk proteins as well some undefined proteins. The study resulted in the characterization of a-lactalbumin (related to c-type lysozymes), whey acidic protein (a cysteine rich protein-related to neurpohysins, antiproteases and some other biologically active peptides), and a fragment of B-casein (a praline rich peptide with relationship to opioid like peptides). A brief account of the proteins studied is given below.
1-1a-Lactalbumin.
The complete amino acid sequence of camel milk a-lactaloumin was determined by analyses of the intact protein, the CNBr fragments and the enzymatic peptides obtained from the carboxymethy protein. Results show that the protein consists of 123 amino acid residues with a quite homologous to other characterized a-lactalbumins but also exhibit extensive differences: 35 residues are conserved in hitherto known a-loctal-bumins with characterized structures. All residues important for structural or functional roles are conserved in camel a-lactalbumin.
1.2Whey acidic protein.
A protein (M 14 kDa) rich in Cysteine/ÃÂÃÂÃÂÃÂ½ cystine has been isolated from camel milk by exclusion charomatography and reverse-phase high performance liquid chromatography. The complete amino acid sequence of this protein has been determined by the analyses intact protein and peptides obtained form CNBr, trypsin, glu specific protease and cleavage after tryptophan residue from the carboxymethylated protein. The protein has 16 cysteines in a total of 117 amino acid residues corresponding to 8 disulphide bridges.
Comparision of the protein with some other proteins reveals interesting relationships: (1) the protein is homologous to previously reported rat and mouse protein, (ii) it shows a region with postulated phosphoserines in relation to a- and B caseins; (iii) demonstrate some similarities to neurophysins and antileukoprotease in half cysteine and internal repeat pattern and to a domain of red sea turtle protease inhibitor and (iv) superficial similarities to insuline family and to some other biologically active proteins are observed.
1.3The results identify the protein as a member of whey acidic proteins classified in the family of ÃÂÃÂ¢ÃÂÃÂÃÂÃÂFour disulphide coreÃÂÃÂ¢ÃÂÃÂÃÂÃÂ proteins and extend suggestions of relationships with various proteins involed in binding or interacting functions.A B-casein Fragment ( a protine rich peptide form camel milk)
A camel milk protein has been purified by reverse phase HPLC. The protein is rich in praline (25% of the whole protein). The N-terminal amino acid sequence shows that the protein is homologous with a C-tertminal region of B-caseins from other species. The protein is concluded to be fragment of B-casein derived form non-trytic type of cleavage of the parent molecule.